PM regression with commit 5de85b9d57ab PM runtime re-init in v4.5-rc1

[tony@atomide.com (Tony Lindgren)]

Hi,

* Ulf Hansson <ulf.hansson@linaro.org> [160202 02:43]:
> 
> For the omap_hsmmc and likely also other omap drivers, which needs more
> than one attempt to ->probe() (returning -EPROBE_DEFER), this commit
> causes a regression at the PM domain level (omap hwmod).
> 
> The reason is that the drivers don't put back the device into low power
> state while bailing out in ->probe to return -EPROBE_DEFER. This leads to
> that pm_runtime_reinit() in driver core, is re-initializing the runtime PM
> status from RPM_ACTIVE to RPM_SUSPENDED.

Yup, that's the bug here. It seems that we never call the runtime_suspend
callback at the end of a first failed device driver probe if the driver
has set pm_runtime_use_autosuspend. Only rpm_idle runtime_idle callback
gets called. So the device stays on.

This does not happen if pm_runtime_dont_use_autosuspend() is added to
the end of the device driver probe before pm_runtime_put_sync().

> The next ->probe() attempt then triggers the ->runtime_resume() callback
> to be invoked, which means this happens two times in a row. At the PM
> domain level (omap hwmod) this is being treated as an error and thus the
> runtime PM status of the device isn't correctly synchronized with the
> runtime PM core.

That's a valid error though, let's not remove it. The reason why we
call runtime_resume() twice is because runtime_suspend callback never
gets called like I explain above.

> In the end, ->probe() anyway succeeds (as the driver don't checks the
> error code from the runtime PM APIs), but results in that the PM domain
> always stays powered on. This because of the runtime PM core believes the
> device is RPM_SUSPENDED.

FYI, the following allows runtime_suspend callback to get called at the
end of a failed driver probe so the hardware state matches the PM runtime
state. Need to debug more.

Regards,

Tony

8< ------------
--- a/drivers/mmc/host/omap_hsmmc.c
+++ b/drivers/mmc/host/omap_hsmmc.c
@@ -2232,6 +2232,7 @@ err_irq:
 		dma_release_channel(host->tx_chan);
 	if (host->rx_chan)
 		dma_release_channel(host->rx_chan);
+	pm_runtime_dont_use_autosuspend(host->dev);
 	pm_runtime_put_sync(host->dev);
 	pm_runtime_disable(host->dev);
 	if (host->dbclk)